The present invention relates to a balloon catheter, and in particular, though not limited to a balloon catheter of the type for determining the volume and/or transverse cross-sectional diameter or area of a vessel, lumen, sphincter or stoma. The invention also relates to a catheter, and to a method and apparatus for monitoring the transverse cross-section of a stoma, and particularly for monitoring the transverse cross-section of a stoma during formation of the stoma, for example, during the formation of a stoma in a stomach. The invention also relates to a method for forming a stoma in a vessel.
Balloon catheters, in general, comprise an elongated catheter which extends between a proximal end and a distal end. An inflatable element, typically a balloon is located at the distal end of the catheter with the catheter extending through the inflatable element, so that the inflatable element defines with the catheter an annular hollow interior region extending around the catheter. A lumen extends through the catheter from the proximal end thereof to the inflatable element and communicates with the inflatable element for accommodating an inflating medium to and from the inflatable element for inflating and deflating the inflatable element. Measuring electrodes may be provided on the catheter for facilitating measuring of the transverse cross-sectional area and/or diameter and the volume of the inflatable element, and in turn, for measuring the transverse cross-sectional area and/or diameter and the volume of a lumen or vessel within which the inflatable element is located and inflated therein.
Such balloon catheters are used for carrying out an investigation or a procedure at a remote site in the human or animal body. For example, balloon catheters are used for determining the transverse cross-sectional area or diameter of a lumen or vessel, and are also used for determining the volume of all or a portion of a lumen or vessel. Such a lumen or vessel may, for example, be the oesophagus of a human or animal subject, a stomach or a part of a stomach, for example, a part of a stomach resulting from a bariatric procedure in a human or animal subject. Such balloon catheters are also used for determining the degree of relaxation of a sphincter, as well as the muscle tone of a sphincter, for example, the lower oesophageal sphincter of a subject. Needless to say, balloon catheters may be used for determining the transverse cross-sectional area, diameter and/or the volume of a lumen or vessel or a sphincter in any part of the gastrointestinal tract. Such balloon catheters are also used in the vascular and cardiovascular system of a human or animal subject for determining the transverse cross-sectional area and the volume of all or part of a vessel or lumen. Additionally, such balloon catheters are used for carrying out procedures at remote locations, for example, dilating an occlusion in a lumen or a vessel, and ablating tissue at a remote location in a lumen or a vessel.
However, in low pressure applications of such balloon catheters, in particular when a balloon catheter is used for determining the transverse cross-sectional area and/or the volume of a lumen, a vessel or a sphincter, it is essential to be able to accurately monitor the actual pressure within the inflatable element of an inflating medium which is used to inflate the inflatable element of the balloon catheter. This is particularly so when the inflatable element is being inflated to just fill the cross-section of the lumen or vessel, and when the pressure of the inflating medium is being monitored in order to determine when the inflatable element just fills the cross-section of the lumen or vessel. In general, known methods and systems for determining the pressure of the inflating medium in the inflatable element of a balloon catheter require monitoring the pressure of the inflating medium at the proximal end of the catheter. In other words, the pressure of the inflating medium is monitored at the location at which it is being delivered to the inflating medium accommodating lumen of the catheter. This is unsatisfactory due to the remoteness of the proximal end of the catheter from the inflatable element. By virtue of the fact that the proximal end of the catheter is remote from the inflatable element, in general, the pressure of the inflating medium read at the proximal end of the catheter does not accurately represent the pressure of the inflating medium in the inflatable element, due to the fact that a pressure drop occurs along the lumen between the proximal and distal ends thereof.
This is particularly so where the catheter of the balloon catheter is of relatively small transverse cross-sectional area in order to gain access through vessels and lumens of correspondingly small transverse cross-sectional area, in such catheters, the lumen which accommodates the inflating medium to the inflatable element is of proportionately small transverse cross-sectional area. The smaller the transverse cross-sectional area of the lumen through which the inflating medium is accommodated to and from the inflatable element, the greater is the pressure drop in the inflating medium accommodating lumen between the proximal end of the catheter and the inflatable element. Thus, in catheters of small transverse cross-sectional area a pressure reading taken of the inflating medium adjacent the proximal end of the inflating medium accommodating lumen does not accurately represent the pressure of the inflating medium in the inflatable element due to the pressure drop between the proximal end of the inflating medium accommodating lumen and the distal end thereof adjacent the inflatable element.
Furthermore, during inflating and deflating of the inflatable element, the pressure drop across the inflating medium accommodating lumen between the proximal end of the lumen and the distal end adjacent the inflatable element becomes significantly greater, and thus, a reading of the pressure of the inflating medium adjacent the proximal end of the inflating medium accommodating lumen would fail to produce an accurate indication of the pressure of the inflating medium within the inflatable element. Accordingly, there is a need for a balloon catheter which addresses this problem.
In such balloon catheters which comprise a plurality of axially spaced apart measuring electrodes located on the catheter within the inflatable element, the measuring electrodes, in general, are band type electrodes which extend around the catheter. In general, two of the measuring electrodes, namely, the two outermost electrodes are stimulating electrodes for receiving a constant current stimulating signal of known value. The remaining electrodes which are axially spaced apart from each other and are located between the stimulating electrodes and axially spaced apart from the stimulating electrodes are sensing electrodes. A constant current stimulating signal is applied to the stimulating electrodes when the inflatable element is inflated with an electrically conductive medium, such as a saline solution. Response voltage signals produced on the respective sensing electrodes in response to the stimulating signal applied to the stimulating electrodes are indicative of the values of transverse cross-sectional area and diameter of the inflatable element adjacent the respective sensing electrodes. By processing such response voltage signals in suitable signal processing apparatus, the values of the transverse cross-sectional area and diameter of the inflatable element adjacent the respective sensing electrodes may be computed. Additionally, once the values of the transverse cross-sectional area of the balloon adjacent the respective sensing electrodes have been computed, by knowing the spacing between the respective sensing electrodes, the volume of the balloon can be computed, and the volume of a part of the balloon between any two sensing electrodes can also be computed.
However, a problem with such balloon catheters is that at locations along the inflatable element where the inflatable element is inflated to a relatively large diameter, the sensitivity with which the values of the transverse cross-sectional area of the inflatable element can be computed is relatively poor. Since the determination of the volume of the inflatable element between two selected sensing electrodes requires a determination of the values of the transverse cross-sectional area of the inflatable element adjacent the respective sensing electrodes which are located between the two selected sensing electrodes between which the volume is to be determined, if the values of the transverse cross-sectional area adjacent these sensing electrodes cannot be accurately determined, it will be impossible to accurately determine the volume of the relevant part of the inflatable element. The reason for the lack of sensitivity with which the values of the transverse cross-sectional area can be determined at relatively large diameters of the inflatable element is as a result of the relatively small voltage drop between adjacent ones of the sensing electrodes, due to the low impedance offered by the inflating medium between the adjacent ones of the sensing electrodes, which are adjacent locations where the transverse cross-sectional area of the inflated inflatable element is relatively large.
Therefore, in cases where a balloon catheter is required to determine the values of the transverse cross-sectional area of a vessel or lumen of varying transverse cross-sectional area, and in particular, where the transverse cross-sectional area varies significantly, in general, it is difficult if not impossible to accurately determine the values of the transverse cross-sectional area of the vessel at locations where the transverse cross-sectional area is relatively large by comparison to other locations of the vessel where the transverse cross-sectional area is relatively small. There is therefore a need for a balloon catheter which addresses this problem.
Catheters are used for accessing remote sites in a body of a human or animal subject such as a remote site in the oesophagus, stomach, and other organs and lumens of the digestive system. Typically, when used for accessing the oesophagus, stomach and small intestine, the catheter, in general, is inserted nasally or orally. When used to access a remote site in the large intestine, bowel and the like, the catheter is entered rectally. Catheters are also used for accessing a remote site in the arterial and venal vascular systems of the human or animal body, and also for accessing a remote site in the cardiovascular system of the human or animal body. However, in the arterial and venal vascular system and the cardiovascular system the catheter, in general, is guided to the remote site along a guide wire. The guide wire is initially passed through the vascular system to the remote site. The catheter is provided with an internal lumen for slideably engaging the guide wire. Once a distal end of the guide wire has accessed the remote site, the internal lumen of the catheter at the distal end thereof is engaged on the proximal end of the guide wire, and the catheter is advanced over and along the guide wire through the vascular system until the distal end of the catheter is located at the remote site. Once the distal end of the catheter is located at the remote site, the guide wire is normally withdrawn through the lumen of the catheter.
To access a remote site in the digestive system, in some cases it is possible to locate the catheter at the remote site without the need for a guide wire to guide the catheter to the remote site. However, in many cases in the digestive system, particularly in the more remote locations, for example, in the intestine, or at locations where the remote site is diseased, or where the catheter must pass through a diseased site in order to gain access to the remote site, it is not possible to guide a catheter to a remote site without the assistance of a guide wire. In many cases, particularly, in the case of a balloon catheter where a number of lumens extending axially through the catheter are required to communicate with an inflatable element, such as a balloon on the distal end of the catheter, the transverse cross-section of the catheter may be such that there is insufficient room for a further lumen to accommodate a guide wire. For example, in the case of a balloon catheter of the type used for measuring the volume or the transverse cross-section of a lumen, a vessel or a sphincter at the remote location, at least two discrete and mutually sealed lumens are required to communicate with the inflatable element. One lumen is required to accommodate wires to axially spaced apart measuring electrodes on a portion of the catheter located within the inflatable element, and a second lumen is required to accommodate an inflating medium to the inflatable element for inflating thereof. In many cases additional discrete and mutually sealed lumens are required, for example, one lumen may be required to inflate the inflatable element with an inflating medium, while another may be required to accommodate the inflating medium during deflating of the inflatable element. In many such cases, with such a number of lumens, all of which require to be sealed there may be insufficient room within the cross-section of the catheter for a further lumen to accommodate a guide wire. Additionally, by virtue of the fact that in such cases all the lumens must be mutually sealed from each other, such lumens are unavailable to accommodate a guide wire. There is therefore a need for a catheter which addresses this problem.
There is also a need for a method for monitoring the transverse cross-sectional area of a stoma in a hollow vessel, for example, a stomach, as the stoma is being formed. Obesity is a serious problem nowadays amongst adults, adolescents, and indeed children. There are many ways of treating an obese subject in order to reduce weight. One such treatment is dieting. However, dieting in seriously obese subjects, in general, has a poor success rate. In such cases surgical procedures tend to be more appropriate. Such surgical procedures, in general, are carried out on the stomach of a subject in order to reduce the size of the stomach, and thereby to reduce the volume of food consumed by the subject. One such surgical procedure is referred to as bariatric surgery during which a gastric by-pass is formed, whereby a portion of the stomach is by-passed. Another such surgical procedure which is referred to as gastric banding requires the formation of a stoma in the stomach intermediate the lower oesophageal sphincter and the intestine. The stoma forms a pouch between itself and the lower oesophageal sphincter in which food is digested. The remaining part of the stomach between the stoma and the intestine becomes ineffective. Thus, gastric banding reduces the effective digestive volume of the stomach, thereby leading to weight loss.
During the procedure to form the stoma, a gastric band is secured around the stomach where the stoma is to be formed. One such gastric band is sold under the Trade Mark LAP-BAND by Allergen, and another such gastric band is sold under the Trade Mark REALIZE BAND by Johnson and Johnson. Such gastric bands comprise a band which is secured around the stomach with a clip adjacent the location at which the stoma is to be formed. An elongated inflatable cuff extends the length of the band, and is located on the band so that when the band is secured around the stomach, the inflatable cuff is located between the band and the stomach. By inflating the cuff with the band secured around the stomach, the cuff acts on the stomach wall, thereby forcing the stomach wall inwardly to form the stoma. The internal transverse cross-sectional area of the stoma is determined firstly, by the amount by which the band is initially tightened around the stomach, and secondly, by the amount by which the cuff is subsequently inflated. Typically, the cuff is inflated by an incompressible fluid, such as a saline solution, and the greater the volume of saline solution pumped into the cuff, the smaller will be the transverse cross-sectional area of the stoma.
It is desirable that the internal transverse cross-section of the stoma when formed is of diameter, which typically lies in the range 5 mm to 15 mm. However, in general, from subject to subject, there is little relationship between the amount by which the inflatable cuff is inflated and the actual internal transverse cross-sectional area of the stoma. This is due largely to the fact that the wall thickness of the stomach varies from subject to subject, and furthermore, the fact that the volume of tissue located within the gastric band will, in general, also vary from subject to subject. A further variable which prevents a relationship being established between the amount by which the cuff is inflated and the actual internal transverse cross-sectional area of the stoma relates to the angle of placement of the gastric band around the stomach.
Thus, since a surgeon does not have access to the interior of the stomach during forming of the stoma, measuring of the internal transverse cross-sectional area of the stoma during inflating of the cuff of a gastric band cannot be carried out. Accordingly, the formation of a stoma in a stomach of a subject is very much a trial and error exercise. Indeed, in general, a subject is required to attend at consultations with the surgeon on a frequent basis after such a procedure has been carried out in order to monitor the progress of the subject and to adjust the amount by which the cuff of the gastric band is inflated in order to alter the internal transverse cross-sectional area of the stoma. Such adjustment can only be made based on a subjective assessment by the subject or the care giver. By further inflating the cuff of the gastric band, the internal transverse cross-sectional area of the stoma is reduced, and by partly deflating the cuff of the gastric band, the internal transverse cross-sectional area of the stoma is increased.
During the surgical procedure to form the stoma, an inflating port for facilitating inflating of the cuff of the gastric band is located adjacent the wall of the abdomen of the subject in order to facilitate inflating and deflating of the cuff at subsequent consultations with a surgeon. Thus, in the event that the stoma is found to be unsuccessful in adequately reducing the volume of food consumed by a subject, the cuff of the band is further inflated in order to reduce the internal transverse cross-sectional area of the stoma. On the other hand, if the effect of the stoma is such as to dangerously depress the appetite of the subject, and in turn, the volume of food being consumed by the subject, the cuff of the gastric band is partly deflated in order to increase the internal transverse cross-sectional area of the stoma.
The need for a subject to attend at frequent consultations with a surgeon subsequent to the carrying out of a procedure to form a stoma in the stomach of the subject in order to set the stoma at the appropriate internal transverse cross-sectional area is undesirable, and furthermore, places a high cost burden on the public health service. There is therefore a need for a method and an apparatus for monitoring the internal transverse cross-section of a stoma in a stomach of a subject and indeed, in any other hollow vessel during the formation of the stoma.
The present invention is directed towards providing a catheter and a balloon catheter which address the problem of catheters and balloon catheters identified above, and the invention is also directed towards providing a method and apparatus for monitoring the transverse cross-section of a stoma being formed in a lumen or vessel, and there is also a need for a method for forming a stoma in a vessel.